In the food packing industry it sometimes happens that a small amount of the food being packed (for example, baby food) will splash onto the finish or threads of the container while the container is being filled. The splashed food will of course spoil if it remains, but normally water washing or spray cooling removes it. However, sometimes food remains lodged in the area between the closure and the container (the so-called "interthread space"), and could present a potential problem. Thus there has been a need for a closure which enables the space between the closure and the container to be washed or flushed clean, after the closure has been applied to the container.
My earlier application Serial No. 402,211, previously referred to, discloses a container closure for that purpose, having internal channels for water washing. In a composite closure embodiment, a lid or insert disk is seated within an annular shell, beneath an overhanging top lip of the shell. Water wash channels are provided on the underside of the top lip of the shell, above the disk, and extend from the inner edge of the lip outwardly over the edge of the insert disk. One or more stops or bearing areas on the underside of the top lip prevent the channels from being blocked and closed by the disk if the closure is overtightened. The wash channels extend past the edge of the disk and communicate with the interthread space, which in turn communicates with an outlet below. Water onto the insert disk of the closure flows through the wash channels outwardly over the edge of the disk and downwardly into the interthread region, to wash out food particles.
However, tiny dust or dirt particles can in theory also pass through the wash channels and into the interthread region, after washing has been completed. The channels at their smallest cross-sections can be very small in size, but smaller particles could conceivably still pass through. If such small dust or dirt particles settled onto the top of the insert disk prior to opening, they could be swept through the wash passages by the in-rush of air into the partial vacuum beneath the disk when the disk is first lifted. Thus the water wash channels, while permitting splashed food to be washed out, nevertheless can permit dirt to be carried onto the surface of the food when the container is later opened.